When we renamed MCS idiopathic environmental intolerances, IEI, at our WHO panel in Spandau Germany, it was largely to deal with these kinds of arguments. Whether a CNS receptor (lambic say) is activated directly by a chemical or other odorant or secondarily through a perception of a hazard and consequent neurophysiological response makes little difference. Stage fright with attendant tachycardia, sweaty palms and even syncope, begins with a psychodynamic process and ends with certain neurophysiological responses. MCS would appear to be similar.

Probably the seminal study is below, demonstrating essentially chance reactivity among patients who believed they chemically sensitive. No physiological basis has been demonstrated to account for extreme claims of odor sensitivity among patients who are not asthmatic or atopic. Environmental activists have inveighed against the toxicity of odorants, and such patients view themselves as canaries in the coal mine; more sensitive than others and bellwethers of our toxic environment. Most of the studies of this population have found very high rates of psychiatric disturbance in such individuals, with somatization, pathological narcissism and sometimes delusional disorders. Many use litigation to manipulate their environment for attention and compensation.

This is not to discount actual allergy, asthma, sensitivity in immunosuppressed individuals, etc., Moreover, I am hardly a fan of the idea that you must pump complex flower-scented hydrocarbons into the air to have a pleasant home. I think we all benefit from living in non-polluted environments. I completely agree with those who would strengthen environmental regulations.

On the other hand, we have to separate the real from the superstitious. Many of these “sensitive” patients demand accommodations down to the atomic level, and report symptoms caused from contact with individuals wearing polyester clothing, reading newspapers, etc. That’s ridiculous. They do not have limbic system neuropathology that renders them unfit to live anyplace but a clean room. They may have severe phobic, paranoid and anxiety disorders, where they attribute their symptoms to a “toxic world.” No filter will eliminate narcissistic, delusional and compensation related demands made by such individuals because their claim of chemical injury is central to their identity and their demands.

Bottom line; we need to care for both groups of people, those with actual physical issues like asthma, and those with severe psychiatric disorders who believe they are being damaged by our industrial society. But helping the latter group does not mean trying to treat somatization, hypochondria, delusions and personality disorder by trying to validate their pathological view of reality. We will never succeed in such an enterprise because there is no physical damage to correct.

Abstract

A clinical algorithm was used to discriminate verifiable chemical sensitivity from psychological disorders in patients referred for evaluation of polysomatic symptoms attributed to hypersensitivity to workplace and domestic chemicals. These patients believed that they were reactive or hypersensitive to low-level exposure to multiple chemicals. Some had previously been evaluated and managed by the tenets of "clinical ecology" and diagnosed as having "multiple chemical sensitivity." Double-blind provocation challenges with an olfactory masker were performed in an environmental chamber on each of 20 patients. A variety of chemicals was employed, one or more per subject, dependent on individual clinical history. Clean air challenges with the olfactory masker were used as placebo or sham controls. As a group, probability analyses of patient symptom reports from 145 chemical and clean air challenges failed to show sensitivity (33.3%), specificity (64.7%), or efficiency (52.4%). Individually, none of these patients demonstrated a reliable response pattern across a series of challenges. Implications for future research in assessment methodology incorporating neurophysiologic and neurobehavioral measures are discussed.

Not sure what your evidence is for "odour sensitivity" being a psychiatric disorder. There certainly is evidence in the literature that it is very real, related to the limbic system reacting to smells, as well as the hazards associated with chemicals used in fragrances.

And that's what I'd recommend as a public health approach: get rid of whatever is causing the smell. If it's people's products, go scent-free. If it's chemicals (e.g., cleaning products), use Ecologo or GreenSeal certified products at least (without the citrus smell chemical that is an asthmagen). If it's not clear what the source is, sounds like it's time for an investigation.

Given that many such individuals who claim odor sensitivity actually have a psychiatric disorder, you are unlikely to find a filter capable of removing somaticized or delusional components from their perception.